Natural attenuation of chlorinated organics in a shallow sand aquifer.

This work presents the second phase of a groundwater remediation program for the migration control of a 1,2-dichloroethane (1,2-DCA) contaminated plume which includes natural attenuation at a distance downgradient from the source area. The conceived system for the plume migration control, implemented just after a major accidental release of 1,2-DCA in the soil, included a 300 m long physical barrier (cement-bentonite diaphragm wall) and 12 extraction wells. Results of field investigations have provided evidence that 1,2-DCA was naturally biodegrading into vinyl chloride as well as ethene under the natural anaerobic-reducing conditions at the site. In that case, source control measures were implemented to accelerate the overall remediation process. Although the results are favorable, the natural degradation of the 1,2-DCA does not guarantee acceptable levels of concentrations. Therefore, a pilot test to evaluate the enhancement of these processes is being carried out through the use of a biosparging system. This test is being implemented near the source to achieve sequential aerobic-anaerobic treatment zones.